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| author | Dave Cheney <dave@cheney.net> | 2014-09-19 02:02:21 +0000 |
|---|---|---|
| committer | Dave Cheney <dave@cheney.net> | 2014-09-19 02:02:21 +0000 |
| commit | 66795e8ba101fc20916196db6d343b0d927e7dd5 (patch) | |
| tree | 803a4a08bce09577c31e0c0cf27327116df8847f /src/runtime/tls_arm.s | |
| parent | 54b63f06478d390d69fc826a16ab19dc6b5d5503 (diff) | |
| download | go-66795e8ba101fc20916196db6d343b0d927e7dd5.tar.gz go-66795e8ba101fc20916196db6d343b0d927e7dd5.zip | |
runtime: fix GOARM<7 build
Update #8690
If liblink determines that the host doesn't support TLS it replaces the MRC call with a BL runtime.tls_read_fallback. The problem is save_g doesn't expect anyone to make any BL calls and hasn't setup its own link register properly so when runtime.tls_read_fallback returns the LR points to save_g, not save_g's caller so the RET at the end of the function turns into an infinite loop.
This fix is only a proof of concept, I think the real fix should go into liblink as its MRC substitution is not as transparent as expected.
LGTM=rsc
R=rsc, minux
CC=golang-codereviews
https://golang.org/cl/143050043
Diffstat (limited to 'src/runtime/tls_arm.s')
| -rw-r--r-- | src/runtime/tls_arm.s | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/src/runtime/tls_arm.s b/src/runtime/tls_arm.s index 7a247ab195..039b013833 100644 --- a/src/runtime/tls_arm.s +++ b/src/runtime/tls_arm.s @@ -29,7 +29,13 @@ TEXT runtime·save_g(SB),NOSPLIT,$-4 MOVW g, R0 // preserve R0 across call to setg<> RET #endif + // If the host does not support MRC the linker will replace it with + // a call to runtime.read_tls_fallback which jumps to __kuser_get_tls. + // Both functions are written to only disturb R0 so it should be safe to + // use R11 here to temporarily store LR. + MOVW LR, R11 MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer + MOVW R11, LR // $runtime.tlsg(SB) is a special linker symbol. // It is the offset from the TLS base pointer to our // thread-local storage for g. @@ -51,7 +57,10 @@ TEXT runtime·load_g(SB),NOSPLIT,$0 // nothing to do as nacl/arm does not use TLS at all. RET #endif + // See comment in save_g. + MOVW LR, R11 MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer + MOVW R11, LR // $runtime.tlsg(SB) is a special linker symbol. // It is the offset from the TLS base pointer to our // thread-local storage for g. |